Modern wireless communications networks employ different access techniques when a first network component intends to access a second network component. As an example for such access techniques the so-called random access (RA) scheme can be mentioned. The name “random access” indicates that access requests are generated in a random manner from the point of view of a network component receiving the access requests.
An exemplary RA scheme is specified by the 3rd Generation Partnership Project (3GPP) in section 6 of the 3GPP document TS 25.214, Version 4.4.0 (2002-03) titled “Technical Specification Group Radio Access Network; Physical Layer Procedures (FDD); Release 4”. Another exemplary RA scheme has been defined by standardization bodies for the Global System of Mobile Communications (GSM).
In RA schemes there may arise the situation that several network components simultaneously try to access a specific further network component, i.e. that access requests of different network components “collide”. Such collisions are detrimental to the quality of service since they result in access delays, message losses, etc. Consequently, various techniques have been introduced to avoid or reduce the detrimental effects of collisions inherent in RA schemes.
For example it has been proposed to implement slotted repetition schemes according to which a specific network component repeatedly transmits its access request until it receives an acknowledgement from another network component. Furthermore, collisions may be avoided or reduced by providing a technique that allows to differentiate between access requests of different network components. To that end each access request may comprise a particular identification code, also called “random discriminator” (GSM) or “signature” (3GPP), which allows a network component that receives two or more access requests simultaneously to discriminate between random access requests of different network components. A third way of reducing collisions inherent in RA schemes is to group the network components into specific access classes. The definition of such access classes allows to prohibit whole populations of network components the transmission of access requests based on their membership to a specific access class.
All these mechanisms help to avoid or reduce access delays and other detrimental effects of colliding access requests typical for RA schemes. However, such collisions are not the only source of e.g. access delays. Another source are for example too low power levels of the access request signals. Too high power levels, however, unnecessarily increase the overall interference level and reduce the system capacity.
This demonstrates the need for efficient power control mechanisms. In general, power control refers to the possibility to control within a specific range the transmit power of individual network components. An exemplary power control mechanism for the transmission of access request signals within RA schemes is described in Matthias Schulist, Georg Frank, “Link Level Performance Results for a WCDMA Random Access Scheme with Preamble Power Ramping and Fast Acquisition Indication”, Proc. of VTC'99.-Fall. According to this power control mechanism a specific network component repeatedly transmits its access request signal using a power ramping technique. Starting at a properly chosen initial power level, successive access request signals are transmitted at increasing power levels until they are detected by a network component which has the task of access management.
In response to receipt of an access request signal the network component having the task of access management has to signal to the network component which issued the request whether the request is granted or denied. To this end an access control signal has to be generated and transmitted.
To choose an appropriate transmit power level for the access control signal is an operator's choice which influences the capacity of the network component that transmits the access control signal. In order to ensure a sufficiently high detection probability of the access control signal, the access control signal will usually be sent at a comparatively high transmit power level.
There is a need for an effective signaling mechanism between a network component requesting access to a node of a wireless communications network and another network component controlling the access.